Beryllium alloy

ABSTRACT

THE ALLOY IS PREPARED BY ADDING TO THE BERYLLIUM 0.05% TO 3% BY WEIGHT OF CALCIUM AND 0.15 TO 3% BY WEIGHT OF AT LEAST ONE ADDITION METAL SELECTED FROM THE GROUP COMPRISING IRON, PALLADIUM, GOLD, PLATINUM, IRIDIUM, RHODIUM, THE REMAINDER BEING ESSENTIALLY CONSTITUTED BY BERLLIUM, THE PRODUCT OBTAINED BEING SUBJECTED TO A HEAT TREATMENT OF 1 TO 10 HOURS AT 750-1000*C. FOLLOWED BY TEMPERING FOR A PERIOD OF 10 TO 200 HOURS AT 500-700*C.

United Smtes Patent 3,685,988 Patented Aug. 22, 1972 3,685,988 BERYLLIUMALLOY Jean-Mathieu Frenkel, Paris, Jean-Marie Logerot, Neuilly, PierrePetrequin, Villebon-sur-Yvette, Robert Syre, Louveclennes, and MichelWeisz, Orsay, France, assignors t Societe Trefimetaux G.P., Paris,France No Drawing. Filed Oct. 2, 1969, Ser. No. 863,327 Claims prority,appliittgioslgfrance, Oct. 9, 1968,

Int. (:1. 6m 25/00 US. Cl. 75-150 8 Claims ABSTRACT OF THE DISCLOSUREThis invention relates to a novel beryllium alloy which is intended foruse at high temperature in an oxidizing atmosphere. This novel alloy isparticularly suited for use in the hot zones of nuclear reactors inwhich the removal of heat is carried out by circulation of carbondioxide gas. The structural elements of a reactor of this type aresubjected to the eflects of elevated temperature, of mechanicalstresses, of corrosion by carbon dioxide gas and of neutron bombardment.

The alloys which have been proposed up to the present time do not provewholly satisfactory. For example, the binary alloy which contains 0.05%to 3% calcium as described in French Pat. No. 1,307,236 granted toAssociated Electrical Industries on Dec. 1, 1961, exhibits satisfactorybehavior in carbon dioxide gas up to 700 C. but reveals in the firstplace that an improvement in the mechanical properties and creepstrength at high temperatures would be desirable and in the second placethat it is rapidly embrittled under the action of neutrons.

As a result of the researches carried out by the present applicant, themechanical properties both at ordinary temperature and at hightemperature as well as the creep characteristics of a beryllium-calciumalloy can be appreciably improved by the addition of a predeterminedquantity of iron, palladium and also of gold, platinum, iridium andrhodium. Resistance to the corrosive action of carbon dioxide gases onthese novel alloys is not affected by the presence of the additionelement, whereas this is not the case of the alloys of the prior art,even when other addition elements are present as in the case of alloyswhich contain both calcium and zirconium, e.g. those described in FrenchPat. No. 1,326,909 granted to Associated Electrical Industries on June27, 1962.

A micrography of a beryllium alloy containing either one or a number ofthe addition elements mentioned above shows a large number ofintermetallic precipitates whose presence within the matrix explains thehardening effect which is obtained.

Embrittlement of beryllium and beryllium alloys under exposure toradiation is caused by gases (mainly helium) which are generated in themetal under the action of neutrons according to the following reactions:

The gas atoms which initially occupy positions adjacent to those of theberyllium atoms from which they are derived migrate and finally collectin the form of bubbles in the grain boundaries and also in the matrix.Under the action of the mechanical or thermal stresses to which the partis subjected in service and if the temperature is of a high order, thebubbles of the grain boundaries will increase in size as a result ofcreation of lattice vacancies and will result in total decohesion of theboundaries.

It is clearly not possible to prevent the formation of these gases; onthe other hand, it is possible to modify the speed at which said gasesmigrate and to delay the moment at which the quantity of gases whichcollect at the grain boundaries becomes hazardous.

One of the objects of this invention is to provide a means for obtainingthis result. The present applicant has in fact found that theintermetallic precipitates set up an obstacle to the motion of gasbubbles within the irradiated beryllium matrix. Moreover, saidprecipitates are correspondingly more eifective as they have a smallergrain size, are more numerous and more uniformly distributed.

The alloys in accordance with the invention can be fabricated by meansof known powder metallurgy techniques, the powder being obtained bycomminution of flakes obtained by lathe turning of cast ingots. Saidingots can be fabricated from a metal which may or may not have beenelectrolytically produced. However, a preferred method of fabricationconsists of vacuum melting followed by direct conversion of the ingot byextrusion, forging or rolling.

The tables given 'below show by way of example the properties of some ofthe alloys which are prepared in accordance with the invention incomparison with those of alloys which are already known. All thesealloys have been prepared from electrolytic beryllium. The alloys A, B,C are not in accordance with the invention; metal A has been obtained bypowder metallurgy and is sintered beryllium. Metal B is an alloycontaining 0.4% Ca in accordance with French Pat. No. 1,307,236; C is analloy containing 0.4% Ca and 0.2% Zr in accordance with French Pat. No.1,326,909.

Alloys D and E are in accordance with the present invention: the alloy Dcontains 0.4% Ca and 0.5% Pd; the alloy E contains 0.4% Ca and 0.2% Fe.

All these alloys except A have been fabricated by vacuum melting in aninduction furnace of a mixture of electrolytically produced berylliumflakes and of previously prepared master alloys Be-Ca, Be-Fe, Be-Pd. Thecast billets thus obtained were then converted to round rods by pressextrusion.

Iron is an inevitable impurity of beryllium and particularly of sinteredproducts since the attrition mills are mostly constructed of steel.However, the iron content does not usually exceed 300 p.p.m. in the caseof electrolytically produced flakes, 800 p.p.m. in the case of thepowder obtained from these flakes and 1500 p.p.m. in the case of apowder obtained from a metal prepared by the magnesiothermic reductionprocess.

The proportions of iron contained in alloys E and F are distinctlyhigher than these values as a result of an intentional addition.

Table I gives the ultimate strengths and the elongations at fracture ofalloys D and E in the extruded state and annealed (one hour at 800 C.)in respect of different temperatures. Very closely related values havebeen obtained in the as-extruded state, in the stabilized state (500hrs. at 575 C.), in the hardened and tempered state. The additions of Pdand Fe increase the ultimate strengths of the 0.4% Ca alloy to a greaterextent than is achieved by the addition of Zr and the same applies 4 toAn, Pt, Ir, Rh. It is possible to obtain even higher of mechanicaltesting is adopted for the purpose of detertensile strength propertiesby increasing the quantity of mining the degree of embrittlement as aresult of neutron Fe, Pd, and so forth which is introduced; however,beirradiation: yond a total quantity of 3% of these elements, the high-Metal irradiated at a dose of 5X10 n.v.t. (total time temperatureconversion of the alloy becomes very difr integrated flux) at 650 C.ficult. J Maintaining an imposed deformation which produces TABLE I aninitial stress equal to the elastic limit of the metal; Ultimate thetest temperature is higher than 600 C. Alloy extruded and strength inElongation at fracture in Aflter the stress has been reheved, a furtherdeforma a a d State J 20 mm- (p w tron 1s applied in order that theelastic limit may again Various b6 attained. pe percent The load cyclesreferred-to above are continued until 0.4 24/40 18/655 125/55 94/100/130 failure of the test sample occurs. The number of cycles 8:: 8:; 2%?1- up to fallure indicates the degree of embrittlement of the 0.4 0.2 Fe28. 5 21 25/32 21/20 1/0205 9.6/34 15 ll'rfldlatefl Beryllium alloyedwith 0.4% Ca and contalmng a small Table II shows the superiority of thealloys in accordproportion of precipitable elements is capable ofwithance with the invention over non-alloyed sintered berylstanding onlyone cycle. lium and a binary beryllium-calcium alloy in regard toBeryllium alloyed with 0.4% Ca containing 1600 ppm. creep h t i ti ofiron is capable of withstanding 5 cycles prior to failure.

The present applicant has also found that, after a heat This testclearly demonstrates the advantage of additreatment which consists indissolving at a relatively low tion elements which give rise tofinegrained intermetallic temperature (750 C. to 950 C.) for a period ofa few precipitates inasmuch as these latter inhibit the coalescencehours followed by tempering for a few tens of hours at of helium in theform of bubbles which are liable to 500-700 C., the alloy exhibits arelatively fine grain result in fracture.

structure and the distribution of the intermetallic pre- What we claimis: cipitates is remarkably fine and homogeneous. 1. A beryllium alloycontaining 0.05% to 3% by TABLE II Alloy Extruded and annealed state CaVarious Stationary creep rate percent percent (10 percent/hr.) Totalelongation in 100 hrs.

A 20/- 20/ 6.3/ 12. 5/ 17.2/ 9.4/- B 0.4 22/ 50/ 6. M Very rapid D 0. 40.5 Pd 19. 5/0. 26 6. 5/0. 07 3. 2/0. 03 78/0. 8 3. 9/0 0 /0. 7 39 0. bE 0. 4 0.2 Fe 14. 3/0. 16 3. 9/0. 05 1. 9/0. 02 0. 4/0. 13 2. 6/0 02 3.0/0. 00 1. 0/0. 01

Test stress in kgx/mrn. 15 12 10 5 2. 5 2 1. 5

Test temperature in C 400 500 600 Table III gives a few of the valueswhich have been weight of calcium and 0.15 3% by weight of at leastfoulldlll respect f grain SiZe, number and SlZe P grams 0f one additionmetal selected from the group comprising precipitate per unit of volumeas compared with the best 4 iron, n di m, gold, platinum iridium rhodiumthe a 1 o 3 J 3 values obtamed the case of the bmary Be ca alloyremainder being essentially constituted by beryllium.

under identical conditions of extrusion.

Further experiments have served to demonstrate that An alloy accordanceWlth clalm rem the this heat treatment did not aiiect either themechanical Proportion of calcium is Within the a g Of 0.3 to 0.8%

properties described earlier or the behavior of the alloy in y g tcarbondi id gas, 3. An alloy in accordance with claim 1 wherein the TABLE IIIAlloys Precipitates Grain Ca Various size Number! Size percent percentHeat treatment mm.

, 120 Small 10-30 0.4 1 hr. 800 C -80 Small 10-30 0.4 0.2 Fe 1 hr. 8000., oil h del Hg plus 24 hrs 00 0. 1 90 10 w 0.1-0.2 0.4 0.2 Fe 1 hr.800 0., oil hardening plus 200 hrs. 600 C 00 10 D 0.10.2 0.4 0.2 Fe 1hr. 800 C. plus 5 hrs. 700 C 00 10 6 o. a

1 Numerous sub-grains.

Several thousand hours of continuous service at opproportion of saidaddition metal is within the range crating temperatures of heavy-watermoderated gas-cooled of 0.15 to 1% by weight. reactors, namely 550650 0,having not substantially 4. An alloy in accordance with claim 1comprising modified either the density or the dimensions of these inter-0.15 to 0.5% by weight of iron. metallic precipitates. 5. An alloy inaccordance with claim 1 comprising The irradiation behavior of thealloys in accordance 70 0.2 to 1% by weight of palladium. with theinvention has been studied. 6. An alloy in accordance with claim 2wherein the 'Embrittlement of irradiated beryllium at hightemperproportion of said additional metal is Within the range ature ismainly exhibited at the time of application of of 0.15 to 1% by weight.a stress which causes an increase in size of the helium 7. An alloy inaccordance with claim 2 comprising bubbles within the grain boundaries.The following method 0.15 to 0.5% by weight of iron.

6 8. An alloy in accordance with claim 2 comprising 0.2 FOREIGN PATENTSto 1% by welght of Palladlum- 1,146,452 3/1969 Great Britain 75-150References Cited L. DEWAYNE RUTLEDGE, Primary Examiner UNITED STATESPATENTS 5 E. L. WEISE, Assistant Examiner 3,145,098 8/1964 Raine et a1.-1 75-150 US. (:1. X.R.

3,169,059 2/1965 Raine et a]. 75-150 17691

